A drawing step is executed to-draw a fiber bundle, called a "sliver" in order to adjust to a predetermined thickness of fibers, which are used as a yarn material. FIG. 3 shows the main part of a draft apparatus D for drawing a sliver S. The draft apparatus D comprises multiple draft rollers, including a front roller 1, an apron roller 2, a middle roller 3 and a back roller 4, arranged in this order from downstream to upstream. The rollers are each composed of a vertically spaced pair includes a top roller t that rotates freely and a bottom roller b that is rotationally driven. The sliver S is sandwiched between the top roller t and the bottom roller b, and the roller speed is set in such a way as to sequentially increase from the input side to the output side, thereby enabling the sliver to be drawn.
Each top roller t for drafting conventionally has a structure such as that shown in FIG. 4. Two bearings 20 and 21 are installed via a spacer 14 on a shaft core 10a formed at both ends of a shaft 10, and a roller cylinder 12 is externally installed on the bearings 20 and 21. The spacer 14 is composed of an outer circumferential spacer 14a and an inner circumferential spacer 14b that can rotate relative to each other, and a C-ring 13 fitted in the outer circumferential spacer 14a is used to position the spacer 14a relative to the roller cylinder 12. The roller cylinder 12 has on the surface of the cylinder body 12a a top cot layer 12b for holding the sliver S. The top cot layer 12b is formed of rubber etc. By fixing a washer 16 to the end surface of the shaft core 10a using a bolt 15, an axial pressure is applied to inner rings 20b and 21b of the bearings 20 and 21 and the inner circumferential spacer 14b to press these components against a pressure-receiving section 10b formed around the base of the shaft core 10a in order to allow the shaft 10 to rotate integrally with the inner rings 20b and 21b of the bearings 20 and 21. An O-ring 11 is mounted on the shaft 10 to prevent the entry of waste fibers etc. In addition, a cap 17 is installed on the end surface of the top roller t.
In the conventional top roller t configured as described above, the bearings 20 and 21 and the inner circumferential spacer 14b are fixed to the shaft 10 in such a way as to form almost no gap. Thus, when the roller cylinder 12 is externally installed on the bearings 20 and 21 and if the shaft 10 and the roller cylinder 12 are decentered relative to each other, the roller cylinder 12 may collide against the outer bearing 21 to effect a large impact force, thereby damaging the outer bearing 21.
In addition, since the outer circumferential spacer 14a generally has a slightly shorter axial length than the inner circumferential spacer 14b, a small gap is formed between the outer rings 20a and 21a of the bearings 20 and 21 and the outer circumferential spacer 14a. Consequently, the roller cylinder 12 may be loosened. When drafting is executed at a high speed to increase the number of rotations of the top roller, the roller cylinder 12 may vibrate, causing non-uniform drafting.